Vibration generating apparatus



May 20, 1958 P. c. EFROMSON 2,835,832

7 VIBRATION GENERATING APPARATUS Filed May 3, 1954 2 Sheets-Sheet 1 IN VEN TOR. PH/L/P C. [FRO 1150A! HTTOR/VE Y5 y 1958 P. c. EFROMSON2,835,832

VIBRATION GENERATING APPARATUS Filed May 3, 1954 2 Sheets-Sheet 2 IN VEN TOR PH/L/P 61 FF/P0446 014/ mmviaw United States Patent ()fiiceVIBRATION GENERATING APPARATUS Philip C. Efrornson, Winchester, Mass.,assignor, by inesne assignments, to The Calidyne Company, Ina, acorporation of Massachusetts Application May 3, 1954, Serial No. 427,131

13 Claims. (Cl. Mil-27) This invention relates to electromagneticvibration generators such as are used in the vibration testing ofmechanical and electrical devices and structures.

As manufactured, heretofore, such generators have comprised a corestructure which is magnetized by means of a direct current winding sothat a high flux concen- L.

tration exists across an air gap in the structure. An armature coil islocated within the air gap and energized from an alternating powersupply so that a reciprocating movement is imparted to the coil andattached armature assembly. suppored by elastic members or ilexuresgenerally in the form of cantilever leaf springs which limit the axialmovement of the armature assembly and maintain the armature coilcentrally within the air gap. These supporting fiexures have their ownnatural periods and modes of vibration which cause unwanted movements inthe armature assembly and increase materially the possibility of flexurebreakage due to fatigue. While it is possible by proper design andoperation of the generator to minimize the troubles caused by suchinherent factors, the leaf fiexures also preclude the possibility ofobtaining a true linear motion of the armature assembly and limit theallowable armature assembly axial motion to relatively short distances.

It is accordingly the principal objects of the present invention toprovide vibration producing apparatus wherein the armature assembly isnot restrained in an axial direction, in which the axial travel of thearmature assembly is a substantially true linear movement, in which thesupports for the armature assembly do not depend upon their elastic orresilient properties and are not subjected to fatigue failures, in whichthe armature assembly supports do not have troublesome periods and modesof vibration, and which advances the art generaily.

According to the present invention, apparatus for producing areciprocating movement of relatively great amplitude comprises a corestructure which is provided with a direct current winding for producinga unidirectional flux across an air gap in the structure. air gap is analternating current coil carried by an armature to which a reciprocatingmovement is imparted. The armature is carried by rotatable supportingmeans such as rollers which constrain radial movement of the armaturewhile permitting t'ree reciprocal movement in an axail direction. In oneaspect the armature comprises a. central rod which extends through anaperture in the core structure and several equally spaced webs whichextend radially between the rod and the armature coil. An attics. atedlinkage is interposed between the armature and the core structure sothat the armature cannot rotate to bring the webs into contact with theadjacent core structure. In another aspect the webs supporting thearmature cell are located outside of the core structure so that thearmature can be rotated with respect to the core.

ln such generators the armature assembly is Disposed in the Cir Theseand other objects and aspects will be apparent from the followingdescription of several embodiments of the invention which refers todrawings wherein:

Fig. 1 is a sectional view of one embodiment of the invention;

Fig. 2 is a sectional view on lines 2-2 of Fig. 1;

Fig. 3 is a sectional view of a second embodiment of the invention; and

Fig. 4 is an enlarged fragmentary view of one of the electricalconnections.

The vibration generating apparatus shown in Fig. 1 comprises a generallycylindrical core structure 10, one end of which is removable as a cover12 to permit a direct current magnetizing winding 14 to be inserted inthe cylindrical recess about the central pole piece 16. The cover 12 hasa central aperture which is sufficiently greater in diameter than thepole piece 16 so that a cylindrical air gap is formed between the wallof the cove aperture and the periphery of the pole piece.

The 'moving armature comprises an alternating current coil 18 carried bythree equally spaced webs 20 which extend radially outward from a rod22, the webs being secured to the rod by bolts 24. The central portion.of each web is cut away to decrease the mass and inertia of thearmature. The rod 22 passes through a central aperture in the corestructure 10, and the pole piece 16 is provided with three radial slots,as is best shown, in Fig. 2, so that the armature is free to move in anaxial direction without interfering with the core structure. The directcurrent winding 14 has a great enough internal diameter and is securedin the annular recess in the core structure 16 by spacers 26 so that theend of the armature coil 18, which extends inwardly through the air gapin the annular recess, passes inside of the coil.

To reduce the mass and inertia of the rod 22 to a minimum it ispreferably made of a relatively light weight material such as aluminumor a suitable plastic. As such materials are relatively soft, twosleeves 28 and 30 of a hardened material such as steel, are pressed overthe ends of the rod 22 to act as bearing surfaces for two sets ofrollers 32 which maintain the rod and armature in a central position inthe core structure. Each set consists of three rollers 32 equally spacedabout the rod 22 intermediate the webs 20 of the armature. Each of therollers 32 is journalled upon one end of a bell crank lever .34 which ispivotally mounted upon a strap 36 secured to the end of the corestructure 10. The radial position of each roller is adjusted by means ofa respective screw 38 which projects through the opposite end of thebell crank 34 to engage a threaded aperture in the strap 36. It will beapparent that with the armature supported by means of rollers 32 thelength of the stroke which can be imparted to a table (not shown) or astructure under test secured directly to the threaded stud 40 in the endof the rod 22 is limited not by the deflection of the supporting meansbut by the length of the coil 18. Furthermore, as the support for thearmature does not depend upon the elastic properties of the rollers 32or their supporting bell cranks 34, the eilect of their periods ofnatural vibration upon the axial movement of the armature is minimized.A linkage 42 is provided to prevent the rotation of the armature aboutthe axis of the rod 22 which would tend to bring the webs 20 intocontact with the walls of the radial slots in the central pole piece 16of the core structure 10. The linkage 42, which extends between the endof the armature rod 22 and the cover 12 of the core structure 10 in aplane passing through the axis of the rod 22, comprises a clevis member44 that is attached to a boss on the cover 12 by means of a cap screw46. The bi- Patented May 20, 1958.

assasaa furcatecl end of the clevis member 44 is pivotally connected toone end of a link 48 by a transverse pin 50. A similar pin 52 pivotallyconnects the other end of the link 48 in a clevis 54 at the lower end ofa second link 56 whose upper end also carries a clevis 58 whichpivotally connects to an extension member 60 bolted on the end of therod.

Alternating electrical power is brought to the armature coil 18 by meansof electrical brushes 62 and 64 which slidingly engage the hardenedsleeves 28 and 30. The brushes 62 and 64 are connected to an externalalter-nating power supply (not shown) by the conductors 66 and 68 andthe sleeves 28 and 30 are linked with the ends of the armature coil 18by conductors (not shown) carried along the rod 22. Alternatively, twoelectrical conductors can be secured.- to the various links of the abovedescribed linkage 42 with a bight at each of the pivotal connections sothat the brushes are eliminated.

A second embodiment of the invention in which the armature is free torotate is shown in Fig. 3. In the second embodiment the core structure80, cover plate 82 and direct'current magnetizing winding 84 aregenerally similar to those described above with respect to the firstembodiment. The armature rod 86, which in the second embodiment ishollow to reduce its weight, likewise extends through an axial aperturein the central pole piece 38 of the core structure 80. The oppositefaces of the core structure are counterbored adjacent the axial apertureto receive the blocks to which the two sets of armature rod supportingrollers 92 are rotatably secured. Although only one roller 92 of eachset is shown in Fig. 3, it is to be understood that each set includesthose rollers which are equally spaced about the rod 86 so that the rodis restrained radially.

At one end or" the rod 86 is carried a coupling 94 with a threadedportion 96 to which a test table (not shown) or the structure to betested are connected. The other end of the rod 86 has a bushing 98pressed thereupon from which project four equally spaced webs 100 toform a spider. Upon the outer ends of the webs 100 is carried a metalring 102 which is stepped so that an insulating ring 104 of a suitableplastic can be pressed thereupon. The insulating ring 104 is the endring of the armature coil 106 which is wound of a square conductor ofsufiicient thickness and stiffness so that the turns are selfsupportingwhen suitably bonded with a conventional cement or varnish. The armaturecoil 106 is completed by a second insulating ring 108 at its oppositeend. The

inner diameter of the armature turns is great enough so .1:

that the coil 106 passes over the central pole piece 88 and lies in thecylindrical air gap between the pole piece and the cover plate 82. Asthe webs 100 of the coil supporting spider are located without the corestructure 80 and the cover plate 82, these do not interfere therewithand the armature assembly is free to rotate.

Although it is possible to bring the electrical connections for thearmature coil 106 through brushes which engage sleeves upon the rod 86as was shown in Fig. 1, the second embodiment employs an alternateconstruction. As is shown in Figs. 3 and 4, an insulating bushing 110 ispressed. into the end of the rod 86. Diametrically attached to the innersurface of the bushing 110 are the respective ends of two flexiblestrips of a resilient electrically conducting strip 112 of a materialsuch as Phosphor bronze. Each of the strips 112 is bent inwardly backupon itself 180 degrees on a relatively large radius so that its endsare in parallel relationship. The innermost ends vare secured to aspacing member such as the insulating rod 114 which is axially disposedwith respect to the hollow armature rod 86. The insulating rod 114 isjou-rnalled in an aperture in an insulated insert 116 which iscentrallylocated man end bell 118 bolted to the cover plate 32. Carriedupon the insulating rod 114 so as to rotate conjointly therewith are twodisks 129 which are I located upon either side of the end bell insert116. Each of the disks 120 carries a slip ring 122 which engages acorresponding slip ring 124.11POD the adjacent end face of the insert116. One of the disks 120 is fixed with respect to the insulating rod114 and the other is free to more axially along the rod (althoughrotating conjointly therewith) so that a spring 126 interposed betweenthe outermost disk and a nut 128 on the end of the rod causes therotating slip rings 122 forcibly to contact the stationary slip rings124.

The rotating slip rings 122 are connected respectively by conductors 130with the ends of the flexible strips 112 attached to the insulating rod114. The ends of the flexible strips 112 attached to the bushing areconnected with the ends of the armature coil 106 by leads (not shown).The stationary slip rings 124 are connected with an external alternatingpower supply (not shown) by conductors 132 so that a circuit to thearmature coil .106.

is completed which includes the conductors 132, the stationary sliprings 124, the rotatable slip rings 122, the conductors 130, theflexible strips 112 and leads (not shown) to the ends of the coil 106.

The insulating rod 114 is held in an axial direction by the end bell118, and the axial movement of the armature relative thereto is pemittedby the bending of the flexible strips 112, the particular portion inwhich the Light is formed varying as the armature moves. Rotation of thearmature is also permitted as the flexible strips 117,, the insulatingrod 114, the disks 120 and slip rings 1 2 rotate conjointly therewith.

it should be understood that the present disclosure is for the purposeof illustration only and that this invention includes all modificationsand equivalents which fall within the scope of the appended claims.

I claim:

1. In apparatus of the type wherein a reciprocating axial motion isimparted to an armature assembly carrying an electrical coil, conductingmeans for connecting the coil with an alternating current power supply,said means including two spaced flexible ribbons of a resilientelectrically conducting material, each ribbon being bent back uponitself at a position intermediate its ends so that the ends thereof liein spaced parallel relationship, one end of each ribbon being attachedto the armature assembly and electrically connected with the coil, theother end of each ribbon having means for electrically connecting theribbon with the power supply, and a spacing member having planarportions for engaging the other ends of the ribbons to act as a supporttherefor which member is relatively stationary with respect to axialmovements of the armature assembly so that, as the assembly is movedaxially, the bend in the ribbon progressively takes place at successiveintermediate positions of the ribbon.

2. Connecting means according to claim l wherein the spacing member isrotatable about the axis of the armature assembly so that the armatureassembly, flexible ribbons and the spacing member can turn as a unitabout the axis of the armature.

3. Connecting means according to claim 2 wherein the spacing member isprovided with two slip rings which cooperate with stationary slip ringsto complete the connection of the coil to the power supply.

4. Apparatus for producing a reciprocating movement of relatively greatamplitude comprising a hollow cylindrical core structure having acentral pole piece one end of which is separated from the remainder ofthe core structure by an air gap, the pole piece having an axiallydisposed aperture therethrough and a plurality of radial slots extendingbetween the air gap and the aperture; a direct current winding formagnetizing the core structure to produce a unidirectional magnetic fluxacross the air gap; an armature having a central rod extending throughthe aperture in the core piece, an alternating current coil positionedin the air gap and a plurality of webs located respectively in the slotsin the core piece and interconnecting the rod and the alternatingcurrent coil; and rotatable supporting means for constraining radialmove ment of the armature while permitting free reciprocal movement inan axial direction.

5. Apparatus according to claim 4 wherein the air gap is defined by thewall of one end or the core piece and the contiguous wall of the portionof the core structure which forms one of the ends of the structure, theinner diameter of the armature coil being greater than the diameter ofthe core piece so that the coil passes over the end of the core pieceinto the cavity within the core structure during the axial movement ofthe armature.

6. Apparatus according to claim 5 wherein the axial length of thearmature coil is several times that of the air gap.

7. Apparatus according to claim 4 wherein a linkage is interposedbetween the armature and the core structure to prevent rotation of thearmature while permitting free reciprocal movement in an axialdirection.

8. Apparatus according to claim 7 wherein the linkage comprises twolinks lying in a plane passing through the axis of the rod, one end ofone of the links being pivotally connected to the rod, one end of theother link being pivotally connected to the core structure, the otherends of the links being pivotally interconnected, and the axes ofrotation of the pivots being disposed normally to said plane.

9. In apparatus of the type wherein an armature assembly carrying anelectrical coil axially moves with respect to a relatively stationarycore structure, conducting means for supplying electrical energy to thecoil, said means including one or more flexible ribbons of a resilientelectrically conducting material, each ribbon being bent back uponitself in a single 180 degree bight intermediate its ends, the ribbonends being disposed in spaced relationship parallel to the axis alongwhich the armature assembly moves, one end of the ribbon being attachedto the armature assembly and electrically connected with one end of thecoil, the other end of the ribbon having means for connecting the ribbonwith an external power supply to impress an energizing potential uponthe coil, said other end being attached to the core structure so that asthe armature assembly is moved axially, the bight in the ribbonprogressively takes place at successive locations along the ribbonintermediate the ends thereof.

10. In apparatus of the type wherein an armature assembly carrying anelectrical coil has a substantially translational movement with respectto a relatively stationary structure, conducting means forinterconnecting the terminal ends of the coil with an external powersupply, said means including two flexible ribbons of a resilientelectrically conducting material, each ribbon being bent back uponitself in a single degree bi-ght intermediate its ends, the ends beingdisposed in spaced planes parallel to the axis along which the armatureassembly moves, one end of each of the ribbons being attached to thearmature assembly and the other ends thereof being secured to thestationary structure so that during movement of the armature assembly,the bights in the respective ribbons progressively take place atsuccessive locations along the ribbons intermediate the ends thereof.

ll. in apparatus according to claim 10 wherein the corresponding ends ofthe ribbons are parallel to and equally spaced from the axis along whichthe armature assembly moves.

12. In apparatus according to claim 10 wherein insulating members areinterposed between the ends of the ribbons and the armature assembly andstationary structure respectively, electrically to isolate the ribbonstherefrom.

13. Apparatus for producing a reciprocating movement of relatively greatamplitude comprising a core structure including a pole piece Whoseperiphery forms one face of a cylindrical air gap, a. field windingencircling the pole piece for establishing a unidirectional magneticllux across the air gap, said pole piece having a central apertureextending therethrough and a plurality of equally spaced slottedrecesses in one end thereof which project radially outwardly from thecentral aperture, an armature assembly including an axially disposed rodwhich passes through the aperture in the pole piece, a plurality of websextending radially outwardly from the rod so as to be located in saidslotted recesses and an alternating current coil positioned in the airgap by the webs, supporting means for the armature assembly includingtwo sets of rotatable members located respectively at the opposite endsof the core structure, each set including at least three rotatablemembers equally spaced circumferentially to engage the rod, and amechanical linkage extending between the core structure and one end ofthe rod to restrain the armature assembly from rotating relatively tothe core structure, said linkage having at least one pivotal joint whoseaxis is normal to the axis of the armature rod so that the linkage doesnot interfere With the reciprocating movement of the armature assembly.

References Cited in the file of this patent UNITED STATES PATENTS839,713 Bijur Dec. 25, 1906 1,333,298 Evershed Mar. 9, 1920 1,808,149Smith June 2, 1931 1,925,659 Giles Sept. 5, 1933 2,118,862 Rayrnent May31, 1938 2,286,897 Costa June 16, 1942 FOREIGN PATENTS 903,046 FranceJan. 5, 1945

